In fusion reactors hydrogen isotope permeation through fusion reactor components, such as first walls and limiters, pose serious recovery and environmental problems due to radioactivity. Any permeation barrier for the first wall must be with coolants such as helium, water or liquid metals. One of the most attractive compatible means of reducing permeation is to introduce a permeation barrier in the form of a coating on one side of the component that does not face the hydrogen source. Oxide materials are extremely attractive for this application since they have the lowest known permeabilities for hydrogen. However, application of an oxide coating to the metallic substrate is limited by the thermal, mechanical and metallurgical incompatibilities between the phases being joined. In general, the bonding and mismatch in expansion between the oxide and metal severly limit the choice of materials. In addition, variations in coating uniformity, porosity, flaw distribution, etc., create serious coating reliability problems, especially if complex geometries are to be protected. Finally, such coatings are not self healing and could create serious hydrogen leakage problems in the case of coating failure.